Ferraris type torque system for current-responsive time relays



Dec. 3, 1957 R. BRAUN 2,815,471

FERRARIS TYPE TORQUE SYSTEM FOR CURRENT-RESPONSIVE TIME RELAYS Flled July 8 1955 BY JWHMMN W ATTORNEYS United States atent FERRARIS TYPE TORQUE SYSTEM FOR CURRENT-RESPONSIV E TIME RELAYS Roland Braun, Nussbaumen, Switzerland, assignor to Aktiengesellschaft Brown, Boveri & Cie., Baden, Switzerlaud Application July 8, 1955, Serial No. 520,857

Claims priority, application Switzerland February 16, 1955 5 Claims. (Cl. 317-167) This invention relates to relays and more particularly to those of the Ferraris type which include a disc that is set into rotation Whenever the current being monitored reaches a predetermined response or threshold level. To

avoid the necessity for transmission gearing, the disc is arranged to rotate so slowly that the desired relay time is obtained in less than one complete revolution of the disc as a function of the time the current remains above the response level, and the relay contacts, usually associated with the shaft on which is mounted the disc, are actuated after a predetermined angle of rotation of the disc. A restoring spring arranged to exert a countertorque on the shaft serves to bring the disc back to its starting position.

For causing the disc to rotate in response to the overcurrent, a magnetic system is utilized which includes a laminated iron core having a coil winding thereon adapted to be energized by the current, and a pair of legs terminating in a pair of confronting pole shoes located adjacent opposite faces of the disc near the periphery of the disc. It is also conventional to associate a shortcircuited coil with each pole shoe.

As previously indicated, the disc is arranged to rotate through not more than one revolution and at a very slow speed, in order to avoid use of transmission gearing. Up to now this requirement has been met by use of a disc having a relatively large diameter which latter essentially determines the overall physical dimensions of the relay.

The time-current characteristic of Ferraris type relays approach a hyperbolical curve. The magnetic cores used in relays of conventional construction have an approximately uniform cross-sectional area or their area is smallest inside of the coil, and saturation of the core will be reached, even in the case of high amplitude currents, over a short magnetic path only, while the core portions adjoining the pole shoes will remain unsaturated. The decrease in magnetic flux towards the pole shoes is caused, in magnetic cores having an air gap of several millimeters between the pole shoes, by the magnetic leakage field which, emerging from the magnetic core, has the effect of diminishing proportionally the magnetic flux towards the pole shoes.

According to the present invention, the magnetic iron of the core is given a sectional area which tapers off, i. e. decreases, from the location of the coil towards the pole shoes so that as to coil currents above the response level, the iron will be magnetized almost over its entire length to the saturation point; also the sectional area of the pole shoes is preferably more than thrice that of the iron leading to the pole shoes, i. e. at the junction of the tapered legs of the iron core with the pole shoes and Whereat the legs have their minimum cross sectional area.

It is a further advantage of the invention if the decrease in sectional area of the iron in the direction of the pole shoes is approximately proportional to the decrease in magnetic flux caused by leakage from the core.

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The flux through the iron, as it becomes generally weaker, will now, because of the narrowing sectional area of the iron, produce an almost uniform magnetic induction through the entire pole.

The invention will now be more particularly explained with reference to a practical embodiment thereof shown in the accompanying drawings wherein:

Fig. l is a view in perspective of the improved Ferraris type relay;

Fig. 2 is also a view in perspective of a portion of the magnetic core of Fig. l modified to include means for making adjustments in the sectional area of the iron; and

Fig. 3 is a graph showing the variation of coil current with time.

With reference now to the drawings and to Fig. 1 in particular, the Ferraris relay is seen to include a magnetic core having one leg around which the coil 2 is placed, the coil being adapted for energization in accordance with the amplitude of the current to be monitored. The core leg is constituted by a pair of parallel spaced sets 1a, 1b of laminations, the sets of laminations being separated by the end portions of laterally extending laminated core legs 10, 1a which are interposed between the ends of the lamination sets 1a, 1b. The ends of lamination sets 1a, 1b with the ends of the core legs 10, 1d are secured together by studs 3.

The opposite ends of the core legs 1c, 1d terminate respectively in laminated pole shoes 4a, 4b confronting each other and positioned adjacent opposite faces of the circular disc 5 at its peripheral portion, the disc being mounted for rotation about its center on an axle 6 with which the relay contacts (not illustrated) are associated. The cross-sectional area of each pole shoe, 4a, 4b is much larger, and preferably more than three times larger than that of the core legs 10, 1d leading to the pole shoes. That is to say, the tapering core legs 10, id have their minimum cross section at the junction with the pole shoes 40, 4b, and the cross sectional area of the shoes is thrice that of the minimum cross section of the core legs 10, 1d. Each pole shoe has associated with it a short-circuited winding or turn 7a, 7b respectively.

It will be noted that the cross-sectional area of the core legs 1c, 1d decrease progressively at the outer portions thereof in the direction of the pole shoes to the end that in case of currents above the threshold response level, the iron in the core legs will be magnetized over its entire length to the saturation point. Preferably the decrease in cross-sectional area in the core legs 10, 1d is made approximately proportional to the decrease in magnetic fiux caused by leakage from the core. The magnetic flux through the iron core, as it becomes gradually weaker will now, because of the narrowing sectional area of the core legs 1c, 1d, produce an almost uniform magnetic flux or induction throughout the entire pole.

The very large area of the pole shoes 4a, 4b in comparison to the adjoining portions of the core legs 10, 1d serves to establish a large air gap area at the disc face and hence a very small air gap resistance to magnetic fiux in order to keep the number of ampere-turns on coil 2 as small as possible. When the current rises, the saturation will be distributed quite uniformly over a large portion of the magnetic path thereby greatly limiting the increase in the flux effect and consequently of the torque. The torque will increase with an increase in current in such proportion only as it is required for a small disc diameter in accordance with the desired time-current characteristics. In this manner it is possible to use discs having a diameter as small as 7 centimeters and less, and by arranging the disc shaft or axle 6 vertically, to also keep the width of the relay case which houses the operating parts correspondingly small.

Spaced studs 8 associated with both core legs 1c, 1d

serve to fasten the magnetic system to the frame (not illustrated). By fastening the core legs directly to the frame it becomes possible to exchange the coil 2 without moving the pole shoes.

Fig. 2 illustrates a modified construction for the coil leg of the core, the coil being omitted in this view for clarity in understanding the construction, which enables one to make adjustments in the sectional area of the core after the relay has been assembled. To this end it will be seen that one or both of the core leg sections 1a, 1b is provided with a longitudinally extending slot 9. A plate 10 of magnetic material is located between and in contact with the core legs 1a, 1b at the general level of the slot 9. A non-magnetic handle 11 attached to the plate 10, the handle 11 being located outside the end of the coil for ease in manipulation, enables one to move the plate 10 up or down with reference to the slot 9 so as to vary the length of the slot left uncovered by the plate and consequently eifect a corresponding adjustment in the sectional area of the core. Such adjustment will allow for inaccuracies attributable to non-uniformity in core material, or core assemblage, as well as for change-overs for example to other frequencies of the operating current.

Fig. 3 shows a time-current characteristic of a torque relay as described above, using a Ferrari's disc with a diameter of 7 centimeters. The current is plotted in multiples of the response current IA, the time in seconds of the maximum time setting. This curve corresponds to characteristics which have been mainly in general use, but which up to now could be obtained without use of transmission gearing only by using discs of much larger diameter.

In conclusion it will be understood that while a practical embodiment of a relay made in accordance with the present invention has been illustrated, various modifications in the construction and arrangement of components may be made without, however, departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. In a Ferraris type relay comprising an iron core having a coil mounted on one leg thereof adapted to be energized by the current to be monitored, said core also including a pair of legs extending from said coil leg and terminating in pole shoes in confronting relation on opposite faces of the peripheral portion of a rotatably mounted disc, the improvement wherein the cross sectional area of said pair of core legs decreases in the direction of said pole shoes from said coil and have a minimum cross section at the junction thereof with said pole shoes thereby to eifect magnetization of said core over substantially its entire length to the saturation point for coil current above the response threshold level, and wherein the cross sectional area of said pole shoes is more than three times larger than the minimum cross sectional area of said pair of core legs at the junction thereof with said pole shoes.

2. A relay as defined in claim 1 wherein the decrease in sectional area of said pair of core legs is approximately proportional to the decrease in magnetic flux caused by leakage from said core legs thereby to efiect substantially uniform magnetic induction throughout said core.

3. A relay as defined in claim 1 wherein said pair of core legs are secured to the frame of said relay thereby enabling said coil to be replaced without moving said pole shoes.

4. A relay as defined in claim 1 wherein the portion of said core on which said coil is mounted is provided with means for adjusting the sectional area thereof.

5. A relay as defined in claim 4 wherein said sectional area adjusting means is constituted by a slot in said core portion and an iron member slidable along the side of said slot to vary the amount by which said slot is left uncovered by said member.

References Cited in the file of this patent UNITED STATES PATENTS 2,306,213 Grave Dec. 22, 1942 FOREIGN PATENTS 368,624 Great Britain Mar. 10, 1932 770,041 France Sept. 6, 1934 

